1. Field of the invention
The present invention relates to a foldable tent frame, and particularly to a foldable dome shaped tent frame made of a synthetic resin, in which tent frame members extend from a central fastening hub in a radiative form, and each of the frame members consists of frame segments joined together through joints, so that the folding and unfolding of the tent would be convenient.
2. Description of the prior art
As shown in FIGS. 2 to 4, the general conventional dome shaped foldable tent frame is constituted as follows.
That is, male and female joint portions 21 and 22 which are made of a synthetic resin are fitted to the both ends of a rod shaped frame segment 20 which is also made of a synthetic resin.
This frame member segment 20 is pivotally joined to another frame member segment 20 by utilizing holes 23 and 24 which are formed on the joint portions 21 and 22 respectively.
Thus when the tent is folded, the frame member segments are folded through the opposite joint portions 21 and 22 in multiple steps. On the other hand, when the tent is unfolded, the frame member segments 20 form arcuate poles, and the male and female joint portions 21 and 22 form strong joinings with the joint portions 21 and 22 of an adjacent frame member segment 20, thereby strongly supporting the tent in a dome shape.
However, in order to ensure convenience and to maintain the elasticity and strength of the tent frame, the joint portions 21 and 22 are not provided integrally with the frame member segment 20, but are formed in the following manner. That is, the frame member segments are formed by cutting an extruding rod by a certain length, and then, the joint portions made of a synthetic resin are formed on the ends of the frame member segment by being inserted into a molding die.
As shown in FIG. 3, the attachment of the opposite joint portions 21 and 22 to the frame member segment is carried out in the following manner. That is, first one end of the frame member segment 20 is inserted into a joint portion molding die 25, and a synthetic resin is injected into the molding die 25 to form the joint portion 21, while the other end of the frame member segment is let to undergo the same process, thereby integrally attaching the joint portions 21 and 22 to the opposite ends of the frame member segment 20.
However, according to this attaching method, the end portions of the frame member segment is smoothly cylindrical as shown in FIG. 4, and therefore, when the tent is repeatedly used by folding and unfolding the tent, the frame member segments are repeatedly deflected into an arcuate form.
Therefore, the frame member segments are subjected to deflecting stresses and twisting stresses repeatedly, and therefore, the frame member segments 20 are detached from the joint portions 21 and 22, or the joint portions 21 and 22 are loosely rotated relative to the frame member segment 20.
Consequently, the tent is liable to be easily damaged. Further, if a joint portion becomes loose relative to the frame member segment 20 so as to be rotated by 180.degree., then the relevant frame member segment 20 cannot give an arcuately supporting strength, but the relevant portion is collapsed.
In an attempt to overcome the above described disadvantage, a tent frame was proposed as shown in FIG. 5. As shown in FIG. 5, a rivetting hole 37 is formed on a fitting portion 36 of a frame member segment 30 to which a joint portion 31 is fitted. Then a rivet 38 is fastened into the rivetting hole 37.
In this case, a loose rotation or a detachment of the joint portion 31 can be prevented, but the drilling of the hole and the fastening of the rivet cause the manufacturing cost increased. Further, the drilling of the rivetting hole forms a weak portion on the frame member segment, and therefore, the strength of the frame member segment is weakened, with the result that the life expectancy of the tent frame is shortened.
Meanwhile, FIG. 5 illustrates a constitution as follows. That is, each of the ends 46 of the frame member segment 40 is provided with an L shaped step 47, before forming the joint portions 41. In this case, owing to an planar portion 48 of the step 47, a loose rotation of the joint portion 41 is prevented, but a detachment of the frame member segment in the axial direction cannot be prevented.
Furthermore, the step of the joint portion 41 is formed by simply cutting off the end portion of the frame member segment 40. Therefore, in order to secure a sufficient joining strength, if the end portion of the frame member segment is deeply inserted into the joint portion 41, then the end of the frame member segment approaches the hole of the joint portion too close, with the result that the strength of the portion around the hole is weakened.
In order to avoid this phenomenon, if the end portion of the frame member segment is inserted into the joint portion too little, then the joining strength is decreased and moreover the joint portion would be apt to break off easily.